Selecting the right metrics for farm animal welfare assessment is critical for capturing actual welfare states rather than just measuring inputs that may or may not translate to welfare improvement.
Welfare metric selection determines what welfare assessment actually measures. Input metrics (space per animal, enrichment items provided) are easy to verify but poor predictors of actual welfare - animals in legal-minimum space with mandatory enrichment items may still have poor welfare if management is poor and animals are fearful. Outcome-based metrics measure what matters - whether animals are lame, injured, fearful, well-nourished and able to express natural behaviour. The challenge is that outcome measurement requires skilled assessment and is more difficult to standardise than input verification. Advancing welfare science toward reliable, practical outcome measurement is the most important methodological priority for translating welfare standards into genuine welfare improvement.